Level measuring devices and in particular, transit-time sensors for level measurement, which function according to the radar, TDR, or ultrasound principle, often have highly fluctuating energy consumption, which is brought about by the change from energy-intensive measuring phases and evaluation phases or pause times having a much lower power requirement.
The level measuring devices each have different functional units, which are, in particular, sensor electronics, measuring electronics and the communication circuit. One or more of these functional units normally exhibits a highly fluctuating power requirement. “Highly fluctuating” means that the maximum power consumption of this functional unit is greater than, for example, three times the average power consumption of the functional unit, or is greater than ten times the minimum power consumption of the functional unit.
If such a level measuring device is connected to a two-wire loop, the power consumption is at least temporarily constant and fixed, due to the two-wire operation (4 mA-20 mA or constant current having superimposed digital communication), and the resultant electrical power currently available can be lower than a current power required in the measuring phase.
This results in a buffer being required for energy storage in order to bridge a temporary power deficit. This buffer or energy store is arranged centrally and acts as an energy buffer for all of the functional and circuitry units of the sensor.